Post-tensioning system

ABSTRACT

A POST-TENSIONING ASSEMBLY FOR CONCRET SLABS AND BEAMS IN WHICH AN ANCHORAGE BLOCK FOR A TENDON HAS REINFORCING GUSSETS FACING OUTWARDLY FROM THE CONCRETE SO AS TO IMPOSE COMPRESSING STRESSES THEREIN IN RESPONSE TO TENSION FORCES ON THE TENDON. A PROTECTIVE TUBE IS REMOVABLY SCREW-THREADED INTO AN ANCHORAGE SHEATH AND COVERS THE CABLE AND IS FITTED OVER AN END OF THE TUBE WHICH PROJECTS FROM THE ANCHORAGE TO ELIMINATE FOULING OF THE CONICAL OPENING OF THE ANCHORAGE WITH CONCRETE AND BONDING OF THE CONCRETE TO THE CABLE. THE ANCHORAGE IS SIMPLE AND EASILY FORMED SO THAT A SINGLE ANCHORAGE ACCOMMODATES PLURAL TENDONS.

July 11, 1972 F. M. STINTON ETAI- 3,676,031

POST-TENS IONING SYSTEM Filed May 28, 1970 4 Sheets-Sheet l 5] W, 462%, 4% MW ,4 M

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July 11, 1972 F. M. STINTON E 3,676,031

POST-TENSIONING SYSTEM Filed May 28, 1970 4 Sheets-Sheet 2 fiederz'c M JJZL'IZZWZ/ J5 4 VZZZZa/m M S/aier 775 @m, 7 m'W/y ewe/ @QZZqst July 11, 1972 F. M. STINTON ET AL 3,676,031

POST-TENSIONING SYSTEM 4 Sheets-Sheet 3 Filed May 28, 1970 July 11, 1972 F. M. STINTON ET AL 3,676,031

POST-TENSIONING SYSTEM 4 Sheets-Sheet 4 Filed May 28, 1970 [72067256 7 3 wade 7' do)? 772. AiZZIZZfl MZ/adm AZ 15' @Zere United States Patent C 3,676,031 POST-TENSIONING SYSTEM Frederick M. Stinton, Woodbridge, Ontario, and William M. Slater, Toronto, Ontario, Canada, assignors to Conenco International Limited Filed May 28, 1970, Ser. No. 41,369 Int. Cl. B28]: 7/16 US. Cl. 425-111 9 Claims ABSTRACT OF THE DISCLOSURE A post-tensioning assembly for concrete slabs and beams in which an anchorage block for a tendon has reinforcing gussets facing outwardly from the concrete so as to impose compressing stresses therein in response to tension forces on the tendon. A protective tube is removably screw-threaded into an anchorage sheath and covers the cable and is fitted over an end of the tube which projects from the anchorage to eliminate fouling of the conical opening of the anchorage with concrete and bonding of the concrete to the cable. The anchorage is simple and easily formed so that a single anchorage accommodates plural tendons.

The present invention is directed to improvements in assemblies for post-tensioning concrete slabs and beams.

Present day post-tensioning practice involves the use of tendons formed by cables which extend through the concrete and which are anchored in some way or another within the concrete, After the concrete has been poured and hardened, tension is applied to these tendons so as to impose compressive stresses within the concrete in order to strengthen the same. Usually some form of grommet or the like is placed around the tendons before the concrete has been poured so as to provide a space wherein jacks may be applied to both grip the tendons and apply opposing forces against the concrete and tendons so as to tension the tendons and set up the compressive stresses.

In past post-tensioning assemblies difiiculty has been encountered in preventing concrete from entering into a bore in an anchorage block, or into and around threaded parts of the anchorage assembly and in preventing bonding of the concrete to the cables. If concrete enters such parts, it is time consuming to remove those parts from the anchorage which are initially used for proper positioning of the anchorage. Similarly, if the concrete is bonded to the cables, time and labor must be spent in freeing the cables so that they can be stressed. Also, in prior post-tensioning anchorage assemblies, the an chorages are so formed that voids in the concrete may occur around the bearing face of the anchorage. This is undesirable because this weakens the concrete at the same areas where stresses are imposed by the cables.

The present invention is directed to improvements in tendon and anchorage asemblies for post-tensioning techniques and is particularly concerned with improvements which seal the anchorage and removable fittings associated therewith in such a manner that fouling of concial opening of the anchorage and the threads of the removable parts by concrete is minimized and bonding of the cable 'ice to the concrete is minimized. At the same time the invention provides an anchorage of greater strength while minimizing the presence of voids in the bearing area of the concrete opposed to the anchorage. The various elements employed in the invention and their manner of use reduce the expense of the mechanical elements required, reduce the amount of labor required, and facilitate the post-tensioning process.

These and other objects and purposes will become more apparent in the course of the ensuing specification and claims, when taken with the accompanying drawings, in which:

FIG. 1 is a perspective view of a post-tensioning assembly incorporating the principles of the present invention;

FIG. 2 is a perspective view of another post-tensioning assembly utilizing the principles of the present invention but especially formed to accommodate the use of two tendon cables;

FIG. 3 is an end view of an anchorage element utilized in FIG. 2;

FIG. 4 is an end view of the anchorage element illustrated in FIG. 1;

FIG. 5 is a side view in section, and illustrating anchorage assemblies utilizing the present invention prior to the time that the cable or cables are tensioned,

FIG. 6 is a sectional view of one element which is utilized in the assembly of FIGS. l-S, inclusive;

FIG. 7 is a side sectional view of an elastomeric hole forming element utilized in the assembly of FIGS. 1-6;

FIG. 8 is an end view of a rubber or elastomeric hole forming assembly which is utilized in the assembly of FIG. 2;

FIG. 9 is a cross-sectional view of an anchorage embedded in concrete after various parts illustrated in FIG. 5 and have been removed;

FIG. 10 is a side view of a tube or pipe which is removably attached to the anchorage as illustrated in FIG. 5 and which is removed from the assembly after the concrete is hardened and prior to applying tension to the cable;

FIG. 11 is a schematic view of the invention as applied to a double tendon assembly defined by a looped cable;

FIG. 12 is a perspective view of the cable gripping element illustrated in FIG. 6;

FIG. 13 is a plan view illustrating a modified use of the invention;

FIG. 14 is a side view of the modification illustrated in FIG. 13;

FIG. 15 is a side view illustrating still another modified use of the invention; and

FIG. 16 is an end view of an element utilized in FIGS. 13 and 14.

With specific reference now to the drawings, and in the first instance to FIG. 1, the numeral 20 designates a tendon utilized in imparting compressive stresses to concrete. The tendon 20 is anchored at one end by a first anchorage 21 which is fixed to the tendon.

A second tension applying anchorage is generally designated at 22. Anchorages 21 and 22 are identical. In

FIG. 1 the inner face of the anchorage is seen in the anchorage 21 while the outwardly facing side of the anchorage is presented in the anchorage 22. The anchorages provide relatively smooth plate-like surfaces which abut against the concrete to bear thereagainst and impose compressive stresses therein. As is seen best in FIGS. 1 and 4, the tension applying anchorages 21 and 22 are each defined by an essentially flat bearing plate 23, which extends transversely to the axis of the tendon 20. A central bearing hub 24 projects outwardly from the plate. Reinforcing gussets 25 extend generally radially outwardly from the hub 24 and are integral with both the hub and the plate 23. The gussets 25 are generally triangular in outline as seen in FIGS. 1 and 5. Suitable fillets 26 may be provided between adjacent gussets and the hub for strengthening purposes.

A tube or pipe 27 surrounds the exterior end of the cable 28 which defines the tendon 20 and extends through the anchorage.

The cable 28 is enclosed by a plastic sheath 27a which extends generally throughout the length of the tendon between the anchorages 21 and 22. The sheath 27a freely surrounds the cable 28.

It is preferred to grease the cable 28 within the protective sheath 27a. The protective sheath 27a is adapted to be slip-fitted over an end 27b of the tube or pipe which extends through the anchorage and inwardly therebeyond. This end of the tube is provided with a roughened surface which may be formed by providing screw threads at this exterior end of the tube and thereafter reducing the height of the threads as by grinding. Since the protective tube or sheath 27a is fitted over the inner end portion of pipe 27, the tendency of concrete to enter the space between the cable and the tube 27 is minimized. The sheath 27a is formed from a relatively hard plastic material and serves to enclose and protect the cable 28.

'In accordance wtih the invention, the tube 27 is threaded near the outer end thereof, as at 29, so as to receive .nuts 30 and 31 for positioning the assembly Within a concrete mold defined by form boards. The tube 27 is threaded at a location 32 spaced inwardly from the threads 29 and adjacent the roughened end 27b so that the tube 27 may be threaded into the anchorage. After nut '31 is threaded onto the tube 27, the nut 30 is threaded. on the outer end of the tube and fixed thereto as by welding or the like. Nut 30 then provides a means for rotating the tube 27 while nut 31 provides a movable abutment which is used to secure the assembly in position.

It should be noted that the hub 24 of the anchorage includes an outwardly flared interior opening 33 for a purpose which will be described.

A rubber forming element 34, with a frusto-conical exterior shape and an interior opening 35, is adapted to surround the tube 27 and abut against the end face 36 of the anchorage 22. As is seen in FIG. 7, the elastomeric former 34 preferably has a series of ribs or corrugations 36 spaced along the interior opening thereof so that these ribs may engage the tube 27. The ribs or corrugations 36 seal the elastomeric former against the tube 27 while allowing relatively easy removal of the former from the tube.

When utilizing the present invention, the tendon 20 and anchorages 21 and 22 are inserted within concrete forms which are to receive concrete for a slab or beam and fixed to the forms. The anchorages 21 and 22 are slipped over the cables. The formers 34 are slipped over the ends of the cables and positioned against the anchorages. The ends of the cable are then led out through holes 38 in the form boards. The tubes 27, with nuts 30 and 31 thereon, are then slipped over the ends of the cable, inserted through the holes in the form boards and screwthreaded into the anchorages 22 in the relation shown in FIG. 5. The protective plastic sheath 27a, which surrounds the cable, is then slipped over the inner ends 27b of the tubes 27.

The nuts 30 which are fixed to the tubes 27 are then rotated to thereby rotate the tubes 27 and bring the an- 4 chorages 21 and 22 up snugly against their associated rubber formers 34 and force the formers against the form boards. Nuts 31 are then tightened against the form boards 37 so as to tighten the form board against the assembled anchorages, rubber formers and tubes.

Concrete as designated at 39 is then poured into the forms and imbeds the anchorage, tendon and rubber formers in the position illustrated in FIG. 5 wherein the rubber formers 34 have the outer end faces thereof snug against the forms '37. After the concrete has hardened, the nuts 31 are loosened. The tubes 27 are then unscrewed and removed from the anchorages. The anchorages then hold the tendon 20 in the proper relation.

Rubber formers 34 and the form boards are then removed, which provides a space or hole around the tendon at the ends thereof. Before the jack is applied, strand grip elements '(FIGS. 6 and 12) are positioned in the flared, outwardly facing openings 33 of the anchorages. The strand grip elements are sectionally formed of three pieces and loosely held together by a locking ring 41a which is received in an exterior groove in the pieces which define the elements. These strand grip elements have teeth 42 formed in the interior surfaces thereof, as by a threading operation to enable a firm grip on the cable. The three sections together define a flared interior bore when the sections are in an abutting relation. The several pieces defining the elements provide an outer frusto-conical shape generally matching the frusto-conical opening in the hub 24.

Thus, after the formers 34 are removed, the strand grip 41 is inserted within the matching flared opening of the hub 24, as appears in FIG. 1, and the jack is then applied to exert an inward force upon the concrete, while exerting an outwardly pulling force in the opposite direction upon the exposed end of the cable. This pulls the cable outwardly with relation to the anchorage 21 and sets up tension forces in the cable so as to stress the concrete. When the cable is properly tensioned, care is taken to insure that the strand grip 41 is snugly within the opening 33 and in gripping engagement with cable 28. Thus, when the jack is removed, the tension forces tend to pull the cable 28 and grip 41 inwardly within the anchorage which tightens the grip against the cable and thus results in holding the cable in the tensioned condition. It should be noted that when tension forces are thus applied, the forces impose compressive stresses in the gussets of the anchorage member. This allows use of smaller and lighter weight anchorage member than is the case where reinforcing gussets are subjected to tension forces.

Also, by providing the gussets 25 on the outwardly facing side of the anchorages, any voids in the concrete that are formed in and around the gussets are of no material consequence since this area of the concrete is not the bearingarea of the anchorage against the slab or beam, and since any voids in this area together with the space defined by the former 34 are filled with concrete after the stressing operation. The anchorages provide relatively smooth bearing faces for exerting compressive forces against the concrete between the two anchorages for the cable.

FIGS. 2, 3 and 8 illustrate a modified form of the assembly, utilizing a plurality of tendons 20 positioned side by side and parallel to one another. In these figures end anchorages 43 and 44 are used to support and hold two of the tendons 20. The tension applying anchorages are the same and incorporate the principles of the anchorage illustrated and described with respect to FIGS. 1, 4, 5, 6 and 7, except that they include two hubs, 45 and 46, positioned side by side. Preferably the hubs are positioned so that the walls thereof merge with one another. The hubs include reinforcing gussets 25, extending radially outwardly therefrom, and integral with the bearing plate 47 as is the case in FIGS. 1, 4 and 5. When using the plural tendon structures, in FIGS. 2 and 3, the rubber former has a generally figure-eight shape with interior ribbed openings 49 in a spaced parallel arrangement, as is illustrated in FIG. 8. In essence, the rubber former is defined by two frusto-conical shapes as illustrated in FIGS. and 7, except that wall portions have been cut away and the cut fiat walls abut against one another. In fact it is advantageous to mold two individual formers to form the overall shape shown in FIG. 8 while keeping the two pieces in sliding contact to thereby allow individual placement and removal of each piece.

In use, the assembly illustrated in FIGS. 2, 3 and 8 is assembled as is the case with the assembly of FIGS. 1, 4 and 5, and tension forces are applied after the strand grips are positioned therein, as is the case with FIGS. 1, 4 and 5. The dual anchorage of FIG. 2 may be advantageously used with a single looped cable which defines two tendons as is diagrammatically illustrated in FIG. 11.

The plural tendon arrangement of FIGS. 2 and 8 increases tensioning forces markedly, resulting in savings of labor and material over what is involved with two, totally separate assemblies. A dual tendon structure, as illustrated in FIG. 2, may use tendons with the diameter slightly increased and, with the increased diameter, tension forces are increased markedly.

Increasing the diameter of the cables slightly increases cross-sectional area by a multiple and hence the tension forces which can be sustained by the cables are increased markedly by a small increase in diameter. Thus, a slight increase in diameter of the cables, while utilizing dual cable tendon assemblies as in FIG. 2, may provide tensioning forces equivalent to three separate tendon assemblies of a lesser diameter.

FIGS. 13-16 illustrate use of the invention with cables which are embedded in grout within tubes or ducts. In these figures a dual tendon system is illustrated utilizing the same anchorage 44, threaded pipes or tubes 27, and gripping elements 42 as illustrated in the preceding figures of the drawings. These elements are assembled and placed in forms as previously described. In FIGS. 13 and 14 the cables are enclosed by an elongated metal duct 50 which terminates short of the threads 27b on the rods 27. A metal cap 51 is positioned over the end of the duct 50. Cap 51 has spaced apertures 52 and 53 (FIG. 16) into which small flexible metal tubes 54 and 55 extend. The tubes 54 and 55 are fitted over the threaded ends 27b of the rods 20 and surround a short length of the cables between the cap 51 and the anchorage 44. Cap 51 has an additional aperture 56 in its end face. A plastic grout tube 57 is inserted in this aperture and led to the exterior of the form 37. After the rubber formers 48 and pipes 27 are removed, and the cables are stressed, a fluid grout is pumped through the tube 57 and into the metal ducts surrounding the cables, thus embedding the cables in grout. Air from the interior of the tubes is vented through the strand grips. In this regard the slots between the segments of the strand grips enhance venting of the air. An additional vent (not shown) may be led from the other end of the tube 50 to the exterior.

FIG. 15 illustrates a system using bonded cables as in FIGS. 13 and 14 but with a modified form of enclosing tube. In FIG. 15 a cap 58 is fitted over the end of an enclosure duct or tube 59. Cap 58 is similar to cap 51 except that it has spaced apertures which enable the cap to be fitted over the threaded ends 27b of the pipes in the anchorage and a fitting 58a spaced from the end of the cap to receive grout. A plastic tube 57 is connected to fitting 58a used to introduce grout as in FIGS. 13 and 14.

The anchorages and tubes disclosed herein, whether made for single or double cables, easily accommodate different sizes of cables since the cables are not fixed to the tubes.

The particular interior formation of the rubber formers enables these formers to be applied over the sheath of the tendons very easily because the ribs 36 offer little frictional resistance to sliding movement on the cables 6 and may be compressed slightly during such installation. At the same time the ribs 36 are highly effective in maintaining the proper position of the former during vibration of the concrete before the concrete has set and hardened.

We claim:

1. A post-tensioning assembly for concrete slabs and beams, including an elongated tube having one end portion threaded and the other end portion formed and adapted to receive a protective sheath thereover, said tube having an intermediate portion thereof threaded, an anchorage plate positioned over said tube and having at least one bore threaded on said intermediate portion, an elastomeric hole defining block positioned over said tube adjacent said anchorage plate and between said anchorage plate and said threaded end portion, means on said threaded end portion for rotating said tube within said anchorage, and bearing means between said last named means and said block, said bearing means being threaded on said threaded end portion, whereby the position of said bearing means relative to said block may be adjusted axially of said tube.

2. The structure of claim 1 characterized by and including frictional gripping means on the other end portion of said tube.

3. The structure of claim 2 wherein said block has internal ribs in a bore thereof to provide a gripping relation with said tube while facilitating removal of said block from said tube.

4. The structure of claim 3 wherein said anchorage plate has plural bores therein extending parallel to one another and a tube is received within each bore, each tube being identical and having a hole defining block of the type defined thereon adjacent said anchorage, each tube having said rotating means and said bearing means thereon.

5. A post-tensioning assembly for concrete slabs and beams, including an anchorage plate having a pair of hubs positioned alongside one another and extending from one side of said plate, said hubs having generally parallel bores therein and extending through said plate, an elongated tube extending through each bore and extending on opposite sides of said plate, each tube being threaded in its associated bore, elastomeric hole defining means positioned over each tube adjacent said hubs, the projecting ends of said tubes on the other side of said plates being formed and adapted to receive plastic protective sheaths thereover, the other projecting ends of said tubes having means for rotating the tubes thereon, and bearing means between said hole defining means and each said rotating means and being adjustably positionable along the length of said tubes.

6. The structure of claim 5 wherein each tube has exterior threads between said rotating means and said hole defining means and bearing means are rotatably positioned on said threads to adjustably accommodate varying thicknesses of form boards between said hole defining means and said bearing means.

7. A post-tensioning assembly for concrete slabs and beams, including an elongated cable and means for holdmg one end portion of the cable within a concrete mass, an anchorage assembly positioned on the cable and near the other end of said cable, said anchorage being defined by an elongated tube received over the other end portion of said cable, an anchorage plate received over said tube, said plate being in threaded engagement with an intermediate portion of said tube, said tube having opposite ends extending from opposite sides of said plate with one end within said concrete mass and the other end projecting outwardly from said mass, said other end of said tube having means for rotating said tube thereon and bearing means adjustably positioned along the length of the tube between said rotating means and said plate, said one end of said tube having an end portion of a protective sheath surrounding said cable received thereover.

7 8 8. The structure of claim 7 wherein said first named 2,341,970 2/1944 Worel 24124 means is defined by a second anchorage of the type de- 3,422,586 1/1969 Parrna 25-1l8 T X scribed. 3,447,784 6/1969 Launay 25429.5 9. The structure of claim 7 wherein two cables with 3,399,434 9/1968 Kelley 25118 T X anchorage assemblies of the type described are positioned 5 FOREIGN PATENTS side by side, said anchorage plate having plural bores therein for receiving said tubes, 1,166,941 11/1958 France 249 42 References Cited J. SPENCER OVERHOLSER, Prunary Examlner B. D. UNITED STATES PATENTS 10 TOBOR, Asslstant Examiner 2,069,085 1/1937 Day 24943 X CL 3,163,902 1/1965 Beinburg et al. 24126 z9 4s2; 249 97, 43

Notice of Adverse Decisions in Interferences In Interference No. 98,181 involving Patent No. 3,676,031, F. M. Stinton and. W. M. Slater, POST-TENSIONING SYSTEM, final judgment adverse to the patentees Was rendered Sept. 7, 1973, as to claims 1, 2, 4, 5, 6, 7 8 and 9.

[Oyficz'al Gazette December 25,1973] 

